Motronic advice sought

[Eric Javel <javel001@xxxxxxxxxx>]

My '87 M6 has developed the much-dreaded "no spark" malady.  What I know
so far is that (1) all voltages and resistances at the Motronic
connector are within specs, (2) the injectors deliver fuel properly when
the motor cranks, (3) the coil, distributor, plugs and plug wires are
fine, and (4) +12V reaches the coil.  Thus, it seems likely that the
problem resides in the ECU.

Neither the BMW dealers nor the Bosch service outlets here in
Minneapolis have any way to test/repair ECUs, and they want $885 for a
new one.  I don't feel like spending that kind of money to replace
what's probably a failed $0.50 transistor.  So, my questions are:

1.  Is there something else I should check out before condemning the
ECU?
2.  Assuming the problem is inside the ECU, how do I identify/replace
the failed component?  I've got scopes, etc., and I know my way around
electronic circuits.
3.  Assuming the problem is over my head, does anyone repair ECUs?  If
so, who?
4.  Assuming that repair is impossible and replacement is the only
solution, what's the difference between various flavors of 35-pin ECUs?
Is it just the ROMs with spark timing and injector pulsewidth lookups?
Since not every junkyard has an M5-M6 ECU (part number ends in 079), can
I buy a used one from, say, a 535i and swap my chips into it, or is
there more to the story?

Thanx.


Eric Javel
javel001@domain.elided

------------------------------